as a Vehicle for conveying Heat, 5 1 



much greater, when it is pulled equally, in the direction of 

 the length of its fibres. I found, from the refults of my ex- 

 periments with this fubftancc, that a cylinder of the fize 

 above mentioned, compofed of the ftraight fibres of hemp, 

 glued together, would fuftain 92,000 lbs. vvithout being pulled 

 afunder. 



A cylinder, of equal dimensions, compofed of the ftrongeft 

 iron I could ever meet with, would not fuftain more than 

 66,000 lbs. weight ; and the iron muft be very good not to 

 be pulled afunder with a weight equal to 55,000 lbs. avoir- 

 dupois. 



I (hall not, in this place, enlarge on the many advantages 

 that may be derived from a knowledge of thefe curious facts. 

 I have mentioned them now in order that they may be 

 known to the public; and that ingenious men, who have 

 leifure for thefe refearches, may be induced to turn their at- 

 tention to a fubject, not only very interefting on many ac- 

 counts, but which promifes to lead to moft important im- 

 provements in mechanics. 



I cannot return from this digreffion without juft mention- 

 ing one or two refults of my experimental inveftigations re- 

 lative to the force of cohefion, or ftrength of bodies, which, 

 certainly, are well calculated to excite the curiofity of men 

 of fciencc. 



The ftrength of bodies of different fizes, fimilar in form, 

 and compofed of the fame fubftance, or the forces by which 

 they refill being pulled afunder by weights fufpended to them, 

 ana acting in the direction of their lengths; are not in the 

 fimple ratio of the areas of their tranfverfe fections, or of 

 their fractures, but in a higher ratio, and this ratio is differ- 

 ent in different fubftances. 



The form of a body has a confiderable influence on its 

 ftrength, even when it is pulled in the direction of its length. 



All bodies, even the molt brittle, appear to be torn afunder, 

 or their particles feparated, or fibres broken, one after the 

 other; and hence it is evident, that that form muft be moll 

 favourable to the ftrength of any given body, pulled in the 

 direction of its length, which enables the greateil number 

 of its particles, or longitudinal fibres, to be feparated to the 

 greateft poffible diftance (fttort of that at which the force of 

 cohefion is overcome), before any of them have been forced 

 beyond that limit. 



It is more than probable, that the apparent ftrength of dif- 

 ferent fubftances depends much more on the number of their 

 particles that come into action before any of them are forced 

 beyond the limits of the attraction of cohefion, than on any 



D % fpecilic 



